Category Archives: moisture management

The bathroom corner issue

Once the Thinset mortar behind the waterproofing membranes has cured, we can start with the preparations for the bathroom floor tiles. We had thought about the tiling for a while already, but more on that in another post.

The plan was to start with the base tiles along the floor and wall edges. That lead us head on to a problem that I really wanted to resolve.

Corners in shower stalls are notoriously difficult to seal and to keep clean. This is where the water usually concentrates and soap residue accumulates. In an attempt to manage the concentration of water in those corners, they are often sealed with a bead of silicone, which in turn appears to be a soap residue magnet.

In short, these corners begin to look skanky really fast.

I am not the only one who has been bothered by this. Somebody else actually came up with a solution that makes the corners more hygenic.

This reversed quarter round or cove shaped profile by Schluter with a 18 mm (almost 3/4 inch) radius is made out of rigid PVC and prevents water from concentrating while being easy to clean. It comes in different depths that correspond to the tile thickness with which it will be used.

The anchoring legs of the profile are set into Thinset mortar. Once cured, the base tiles can be installed. They should end up flush with the cove profile to allow for good drainage.

This is one of these obscure gadgets that add to the longevity of an installation, make for a healthier indoor environment, and help with the moisture management.

To control costs, we only installed the cove profile in the shower stall, where it is most needed and most useful. Let’s see if it will do the job and meet our expectations.


1st floor bathroom waterproofing

The shower drain flashing eased my paranoia about moisture management just a little. It will take a waterproofing membrane to put me more at ease.

We have worked with a waterproofing membrane on the floor and walls in the basement bathroom. That experience is good to have under the belt and should facilitate the work in the 1st floor bathroom.

Dual function

There is more to a waterproofing membrane, or liner, that meets the eye at first. The one obvious benefit is about – yes indeed – moisture management! But there is a second and significant advantage of using a liner. It serves as a isolation membrane.

Think about it this way. The tiles are glued to the concrete floor. If there is some movement in the concrete floor, it will develop cracks. These may be minute cracks – hairline cracks. Still, they would propagate all the way to the tile surface.

Because these cracks keep constantly moving, replacing the cracked tiles is really no solution. The new tiles will just keep cracking too.

The liner or waterproofing membrane, which is flexible in nature, will prevent small cracks from propagating from the concrete floor to the tiles, thus the term isolation membrane.

Prioritizing the functions

The concrete floor in the basement bathroom sits on rigid insulation and a sturdy gravel base. It has a very low potential for cracking. The priority there was on the waterproofing function of a liner. The isolation effect was a welcome added benefit. That allowed us to use the relatively thin Kerdi liner by Schluter that was easy to handle.

The concrete floor in the 1st floor bathroom is a very different beast. It sits in between and on top of floor joists. These will expand and contract depending on the temperature and humidity. Plus they react with some level of deflection to the load that is put on them.

Now picture the concrete floor in this assembly. This has high crack potential written over it. The priority here is to isolating the tiles from the floor, with the waterproofing as the added benefit. For this case we opted for the heavy duty 0.8 mm NobelSeal TS membrane.

Liner installation

As with the floor drain flashing, we again use beads of rubber sealant (NobelSealant 150) to waterproof at the overlap of the liner and around the floor drains. We also got nifty corner pieces that we sealed in place with the same product.

Because the walls of the bathroom have a low potential for cracks to develop, we switched back to a lighter gauge membrane, the Noble WallSeal. We place the membrane on the those walls that are exposed to water–behind the lavatory and the toilet, and of course in the shower stall.

Now we are almost ready for the tiles and a handy gadget that goes along with them. More of that in the next post.


Durability and shower drain flashing

Just in case you haven’t figured this out yet, I am paranoid about moisture and water damage in the building.

And I think I have good reason to be, considering what I encountered during the deconstruction process.

Water damage can cause serious durability issues, and durability is one of those underrated principles when it comes to green building practices, even though it is so simple: The longer we can make things last, the less resources they require over time, and the more sustainable they are.

LEED for Homes embraces the durability principle with the inclusion of a “Durability Management Process” in their check list. It gets a little dry, but only for one paragraph!

The process consists of “Durability Planning,” identifying and listing the various durability risk factors, and, “Durability Management,” a quality control for the installed strategies that lower or eliminate durability risks. A third party verification should assure that everything is kosher, and if so, one may earn up to three LEED points.

What did you say? Bureaucratic? Come on, they have to make some money somehow! And only three LEED points, max? Don’t get me started on the points!

For us, as the property owners, occupants, and contractor on this project, durability with or without paperwork, with or without points, is a no-brainer, because it directly affects our short- and long-term bottom line.

Interestingly enough, the durability issues tabulated in the LEED for Homes guidelines are all about moisture control measures (and as I would argue, plain common sense):

  • Tub, showers, and spa areas – Use non paper-faced backer board on walls.
  • Kitchen, bathroom, laundry rooms, and spa areas – Use water-resistant flooring; do not install carpet.
  • Entryway (within 3 feet of exterior door) – Use water-resistant flooring; do not install carpet.
  • Tank water heater in or over living space – Install drain and drain pan.
  • Clothes washer in or over living space – Install drain and drain pan, or install accessible single throw supply valve.
  • Conventional clothes dryer – Exhaust directly to outdoors.
  • Condensing clothes dryer – Install drain and drain pan.
Source: Leed for Homes Rating System (January 2008), ID-2, Table 1, USGBC

What a nice segway back to my paranoia and our shower drain!

Unlike the basement bathroom, the 1st floor bathroom is located above a living space. The floor construction of that bathroom has wooden floor joists that could begin to rot if they get wet (see also images above).

The drain of our walk in/barrier free shower is the most likely point where water could get into the floor assembly and leak into the basement living space. We will waterproof most of the bathroom (stay tuned for the next post), but the drain warrants one additional step, a drain flashing, to further reduce the risk of leakage.

The drain flashing is formed and shaped to perfectly fit onto a floor drain assembly. No awkward folds or stretching, unlike trying to do the job just with the waterproofing membrane.

The drain flashing (NobleFlex Drain Flashing) is sandwiched between the drain base and drain clamping ring. Two beads of rubber sealant (NobleSealant 150) on the drain base prevent water from escaping under the flashing.

Last but not least, I can screw that drain strainer back into the clamping ring and adjust it to the right height, so that I have positive slope to the drain from the entire shower area.

The next step is the waterproofing membrane (NobleSeal TS), which will overlap with the flashing (see drawing above) and is again sealed with two beads of the rubber sealant. More on that in the next post.

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Bathroom cement board

It’s time to put up some walls in the bathroom – which puts me squarely back on one of my favorite building topics: moisture management and indoor air quality (IAQ).

A bathroom, in building science terms, is considered a wet room. Splashes, drips and leaks are inevitable, and can over time lead to structural problems, but also IAQ issues such as mold with negative health impacts on the occupants.

This and any associated durability issues are easy to avoid by falling back onto a few simple moisture management strategies.

One of them is to employ floor drains. We documented the installation of the 1st and 2nd floor bathroom drains in a previous post, and there is more to come in one of the next posts.

Another strategy is to use cement board or fiber cement board as a wall cover in shower stalls, bathtub enclosures, and behind lavatories and toilets.

To give you an idea how water resistant cement board is… I had a leftover piece sitting in the yard for one and a half years, exposed to the elements. It was still in perfectly good shape and I ended up using it for one of our window sills in the basement.

Do not use green board or any other kind of paper-faced gypsum board product. These things are not suitable tile backer products and can turn into big mold traps.

See also Building Science Corporation, Info-306: Interior Water Management

What about the areas that don’t receive tiles, such as the ceiling and the upper half of the wall behind the lavatory and toilet?

Regular drywall will do the job, at the cost of around $6.00 per sheet. The green board products run twice as much (around $12.00 per sheet).

But what about the green board’s mold resistant property? Wouldn’t it prevent mold formation on the walls and in corners? Isn’t that worth the extra cost?

I would say no. Because if a bathroom requires such mold resistant product, there is an insulation/condensation and ventilation issue. And the extra $6.00 per sheet for green board won’t solve those problems, just prolong the denial about the real issues for a little longer.

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No one wants to maintain anything these days. I still get requests for maintenance free landscapes. I wonder when we’ll begin to demand windows that don’t require cleaning or trash that carries itself to the curbside for pickup.

That said, getting in the habit of some simple maintenance tasks can make such a big difference, and in many cases save energy.

Yep, this squeegee helps us to save energy! We possibly won’t get rich over it, but I am a fan of the cumulative benefit.

How? I bragged about our new shower curtain and effective ventilation system in the last post. Rather than turning the ERV into the moisture management workhorse, we use the squeegee to lift the heavy weight.

After each shower, we quickly squeegee off the walls and floor in the shower area. That removes a lot of water that otherwise would need to evaporate and get removed by the ventilation system.

By squeegee-ing that water down into the shower drain, we get away with running the ERV on booster mode for 20 minutes instead of an hour. That’s where it saves us energy.

If you do not have a bathroom fan or a poorly operating one, the squeegee could make a big difference, helping you to manage moisture levels and improving your indoor air quality.



The shower curtain…

… is still missing. You may have read about our salvaged shower wall in the last post, but we still needed a curtain for the front.

I began to poke around online. Lo and behold the search term “recycled shower curtain” actually produced results.

I stumbled across the Bardwil Evolution Shower Curtain. It is, according to the product description, made of 100 percent post-consumer recycled plastic bottles. The bottles are crushed and repurposed into polyester yarn that in turn is woven into the shower curtain.

IAQ (indoor air quality)

I also found an online review that pointed out that this curtain is not as resistant to the onset of mildew as other products and requires washing and bleaching every second week.

Well, that sold me! Why? Because it probably means that the material is not treated with chemicals to prevent mildew and mold – although I don’t know that for sure.

But there is more to it. Mold and mildew on a shower curtain is typically an indicator for poor ventilation in a bathroom. What better way to put our ventilation system to the test!

We have been taking daily showers for the past two months, and there is not a spot on the shower curtain, or a sign of any discoloration which would be the first indicator that something will crop up.

Although we probably should put the curtain in the laundry sometime soon, I really want to keep it up for a little longer just to find out if mildew would eventually crop up.

But so far our ventilation system with the ERV appears to manage the moisture levels in the bathroom just fine.


Belt, suspenders and staples

Regular readers of this blog will know that moisture management is one of my favorite topics. I have now been going for three posts without uttering the word moisture or management and I am beginning to suffer from serious withdrawal symptoms.

To sooth my distress, selfish as it may be, I’ll delight you with some more thoughts on the moisture management topic.

Here in Chicago, depending on your neighborhood, you will begin to hear about basement flooding as soon as the warm season storms roll in. This is not water pouring in through some basement windows, but mostly water backing up into the basement from the city sewer system – Yuck! I had a very close call myself last year.

It was our objective to make the living unit in the basement as flood proof as possible. We came up with a good plan that involved the installation of a check valve. This should take care of the flooding issue.

Still, we may have enough bad luck to get some standing water in the basement, whether it’s because the check valve becomes obstructed or because of a water pipe burst and leak.

Thinking this through – OK, OK, it kept me up at night – we decided to be as prepared as we can.

For instance, almost all of our outlets are about three feet off the basement floor, keeping them a safe distance above any flood water, should it come.


We took some precautions while framing the basement interior. Each interior wall has a cedar stud as a bottom plate. Cedar is a very moisture resistant material and we took the precaution to place it where moisture/water is most likely to occur – right on the basement floor.

We still have one major problem to solve, and that’s the drywall problem. Drywall is not moisture or water resistant at all. Once in contact with a wet spot or water source, it rapidly wicks up the moisture and loses its structural integrity. In other words, it becomes soft, crumbles and needs to be replaced, not to mention the potential for mold growth and deteriorating indoor air quality (IAQ).

We used regular 5/8 inch Type X drywall throughout most of the basement, with a couple of exceptions.

There is the bathroom, which is classified as a wet room in building science terms. Here we used cement board because it is moisture resistant and served as the backer board for the tiles.

And then we have all the interior walls, where we opted for cement board at the bottom (the risk zone) and drywall for the upper portion.


This decision was based on the same rationale we used for the cedar bottom plates.

Moisture or standing water will first show on the basement floor. Because cement board resists moisture absorption, maintains its structural properties even when submerged in water and dries rapidly, we opted to install it along this risk zone.

As one green blogger put it: cement board doesn’t care if it gets wet.

Should we get water in the basement unit, we can ventilate, dry and dehumidify the space and paint over the water marks.  We’ll be in good shape.

With drywall, we would need to rip out and replace all the wall portions that show water damage.

I hope that this investment will pay off, minimizing any IAQ risks and adding to the longevity of the structure .

Well, what I really hope is that we never have to deal with water in the basement.


Bathroom water proofing – walls

A couple of posts back, I talked about the need for moisture management in the bathroom and described the installation of the water proofing membrane on the bathroom floor. Since then, we installed the bathroom ceiling and put up the remaining cement board on the walls.

This means that Cathy can spring back into action and begin with the membrane installation on the walls. We used the same product as we used for the floor, but we were somewhat selective about where we installed it.

The walls most exposed to moisture are in the walk-in shower. These have to be protected by the membrane from floor to ceiling. Cathy extended the membrane by 18 inches beyond the actual shower stall to account for splash that may occur.

The other areas, although not quite as critical because they are only exposed to incidental water, are behind the claw foot tub (not shown in the time lapse), the toilet and bathroom lavatory.

The installation process was the same as for the floor, just on a vertical surface. It went very smoothly and swiftly because of Cathy’s experience gathered during the floor installation.

The membrane will protect us from the frequent as well as the incidental water. As such it will increase the long term durability of the building components and maintain good indoor air quality (IAQ).


Bathroom water proofing – floor

Most good ideas are seeded through communication with experts, like-minded individuals or other interested parties.

The waterproofing strategy in the bathroom was planted by our friend David Lemair. The ideas grew out of an article he referred us to in Fine Homebuilding that talked about barrier free bathrooms.

Because we were dreaming of a walk-in shower, the article was an excellent step by step resource. Unlike the prefabricated shower stalls, a walk-in shower requires particular attention to detail with regard to moisture management. The article helped us to pick the right water proofing strategy and pointed us to suitable products.

Considering our sturdy concrete floor, we opted for a membrane by Schluter called Kerdi. The membrane is sold on a roll that is about three feet wide. We got ourselves 60 feet and Cathy began with the installation on the bathroom floor.

The first step was to wet the concrete floor, which should give us good adhesion for the non-modified thinset mortar. Cathy spread the mortar with a notch trowel and pressed the Kerdi membrane into the thinset bed.

She also carefully folded the membrane up the walls by three inches. This creates a ‘tub effect’ that should help with the moisture management on the floor.

Installing the membrane was hard work. Cathy had to move fast to prevent the thinset from drying out and subsequently loosening its adhesion properties.

It didn’t help that the instructions on the thinset bag reversed the water-to-mortar mix ratio.  Just goes to show that common sense should always prevail.


We came back the next day to cut openings into the Kerdi membrane around the two floor drains. I now could set the drain flange onto the membrane and fasten it to the drain base. Having the Kerdi sandwiched between the drain flange and drain base assures that no water can escape down to the concrete floor. Last but not least we installed the toilet flange.

The better we contain incidental water, the less the risk for long term durability issues and indoor air quality (IAQ) problems.

With the floor done, we can now think of waterproofing the walls where needed.


Bathroom basics

Figuring out the basement bathroom layout happened pretty early on in our project. We needed to know how to route the new sewer system and what drains to put where.

We also learned during the deconstruction process that moisture and water leaks can become a real headache. Bathrooms, in building science terms, are considered wet rooms. There is a whole laundry list of moisture management strategies for bathrooms (or wet rooms) that we researched and wrote about.

Moisture that is not properly managed or contained can lead to sever durability issues and indoor air quality (IAQ) issues, such as mold growth.

One wet room recommendation was to include a floor drain. We actually have two. And no, we don’t have a second one because I am German, but because we opted for a walk-in shower. The concrete floor is already sloped toward the shower drain and floor drain.

Tiles and grout are a good idea on the floor and in the shower area, but they are not water proof. To actually create a water proof environment, it is recommended to use a waterproofing membrane under/behind the tile.

The logical place to start is on the bathroom floor. Whatever membrane we use, we will have to fold it up by a few inches on the walls – walls that are not in place yet.

Well, maybe I should get started on those walls …

Moisture management is often connected to indoor air quality (IAQ). Another moisture management recommendation for wet rooms that helps with the long term IAQ  is to use cement board instead of paperbacked gypsum board (or drywall). Cement board is much more water resistant and less prone to mold growth as it lacks the paper backing component.

The installation involves some puzzling. I have to measure in and cut out holes and openings for the plumbing connections. That took some time, but we got all the openings to fit.

For now I just installed the cement board around the bottom so that we can get started with the water proofing membrane.